An image sensor can be used in low illumination conditions. It can be necessary to amplify the signal from the sensor used in this way. One typical way of doing this is to “bin” the pixels. For example, a group of four pixels is taken together, and handled as a group. This obtains the signal from all four pixels as an increased-level pixel.
A similar issue can exist when high frame rates are used, where each frame of received signal can be integrated only for a relatively short period of time.
High speed readout produces additional similar issues. Specifically, the high speed readout can be read in bursts. Each of the bursts can be for example a unit, e.g., row or a column, of output of the image sensor. Each unit can be associated with its own unit amplifier to allow the effective unit amplification to be carried out faster. However, unit-to-unit fixed pattern noise can result from mismatched in amplifier voltage offset or gain.